In various metallurgical processes such as casting, rolling, forming, etc., the time/temperature profile of the working piece must be precisely controlled. Quenching or cooling media are often used to control temperature, and, accordingly, the cooling power or quenching intensity of these media need to be precisely monitored and controlled.
Furthermore, the heat transfer mechanisms of quenching can change depending on the temperature of the piece being worked. When the surface temperature is much higher than the boiling temperature of the liquid, heat transfer is via "film boiling" in that a continuous film of vapor is maintained between the metal surface and the coolant. In this heat transfer phenomena, the heat transfer rates are relatively low and stable. As the metal surface cools, it will eventually reach a temperature at which the coolant will contact the surface and heat transfer rates will increase rapidly. The heat transfer rates peak during the "nucleate boiling" regime where a large number of steam bubbles are created and easily escape allowing more liquid coolant to come into contact with the surface. As the surface temperature continues to decrease, it eventually cools below the boiling temperature of the coolant and nucleate boiling ceases, heat transfer then is predominantly by convection, and heat transfer rates rapidly decrease.
Quenching media can include water, aqueous solutions of salts or glycols, water/oil emulsions, molten salts, etc. Given the wide range of quenching media available for heat treating processes, a need has developed to measure the quenching intensity of the quenching media throughout the temperature range of a workpiece and initiation of nucleate boiling.
The prior art has provided different systems and devices for evaluating or testing different types of quenching parameters. U.S. Pat. No. 4,636,089 to Schumann discloses a system where a test body is inserted into a bath. The heat energy required to maintain the temperature of the test body constant is used as a measure of the quenching intensity of the bath.
U.S. Pat. No. 4,563,097 to Katafuchi discloses another method for evaluating the cooling performance of a heat treatment agent. In this method, a sensor is placed into a heat treatment agent which is heated to a predetermined temperature. The voltage and current applied to the sensor during the heating step is monitored. A comparison of the acquired data to predetermined data permits an evaluation of the performance of a heat treating agent.
U.S. Pat. No. 4,412,752 to Cellitti et al. discloses a system including a probe and sensor that are heated to a predetermined temperature and then immersed in a quenching medium. Cooling data obtained from the probe and sensor are applied to a computer for comparison with predetermined values.
U.S. Pat. No. 3,620,068 to Cary et al. discloses a testing apparatus for measuring and recording changes in quenching media temperature. The testing apparatus includes thermocouples for sensing temperature of inflowing and outflowing quenching fluid during quenching of a specimen.
It is the purpose of the present invention to provide a method and apparatus for measuring the quenching intensity or cooling power of various liquid media, particularly with regards to water, aqueous solutions and water/oil emulsions during the casting and hot rolling of metals such as aluminum and aluminum alloys. The information obtained from the present invention can be used for quality control, for evaluating different quenching media, and to correlate the effects of changes in operations and quenching media compositions with quenching power for purposes of process improvement and the development of improved quenching media.
The prior art discussed above does not teach or fairly suggest the inventive method and apparatus for measuring the quenching intensity or cooling power of various liquid media which monitors the temperature profile of a heated sample during cooling.